The effect of pharmacologic agents on the modulation of the diurnal pattern of spontaneous uterine activity and of the diurnal variations of the dynamics of the pregnant uterus on the distribution of uteroplacental circulation and fetomaternal exchange will be evaluated in monkeys. Chronically implanted sensors will monitor intrauterine pressure, uterine blood flows, arterial and venous blood pressures, and body temperature. Electronic integration and computer analysis of measured parameters will facilitate evaluation of the studies in an effort to elucidate some of the factors involved in the physiology and control of myometrial contractility and uteroplacental hemodynamics and their influence upon fetal homeostasis. Radioisotopes and other indicators will be used to analyze various aspects of placental and nonplacental uterine blood flow and fetomaternal exchange. A primate breeding colony will be maintained.